New York University professor Paul Light, who has studied the executive branch for decades, thinks much of the blame goes to Congress and what he calls a “Napoleonic approach to defeating the president and reducing big government.”

Light argues that those who oppose new laws are required by the Constitution to repeal them. But he says that has all changed recently.

“If you don’t like a law now, and you can’t repeal it,” Paul says, opponents work to “decapitate the agency and eviscerate its capacity to execute the law.”

Lack of leadership can leave some federal agencies treading water on policy and personnel issues. Sometimes key decisions get put off. And if the president doesn’t have his choices in place, it’s a lost opportunity to effect policy.

Among the agencies operating without permanent leadership:

– The Bureau of Alcohol, Tobacco, Firearms and Explosives, which has not had a permanent administrator since 2006, the year Congress required that the director be confirmed by the Senate.

– The Centers for Medicare & Medicaid Services, which oversees those massive health care programs and hasn’t had a director confirmed by the Senate in seven years. NPR’s Julie Rovner tells Morning Edition that the agency also handles the Children’s Health Insurance Program and now “a big chunk of the Affordable Care Act.” She says in 2011, it handled about 21 percent of the federal budget, or $769 billion.

– The Consumer Financial Protection Bureau. President Obama named Richard Cordray director in a recess appointment in 2011, which is now being challenged in federal court. Cordray has been re-nominated by the president, and his confirmation hearing is set for Tuesday.

– The Federal Election Commission, which has commissioners held over on expired terms.

NPR’s Carrie Johnson says of the nearly 90 federal judgeships currently vacant, about 30 are considered judicial emergencies. “That means the caseloads in those courts are very, very high. And the impact is that judges who are currently on the bench are hearing lots more cases.”

While Senate Republicans are responsible for most of the roadblocks before the president’s nominees now, Democrats have pulled similar moves when it was a Republican president doing the nominating.

Sometimes, the roadblocks aren’t about philosophy or even politics, but rather a senator’s effort to win something for his or her state. For instance, Alaska Republican Sen. Lisa Murkowski is threatening to block Obama’s nominee to lead the Interior Department, Sally Jewell, over construction of a road through a wilderness area that the department opposes.

But those sorts of roadblocks, used as leverage for something a lawmaker wants for her state are relatively rare nowadays, according to NYU’s Light.

“I don’t see as much of that going on,” Light says. “I don’t see a lot of hostage-taking based on personal demands and favors. I see a lot related to just plain anger toward the president, and a reluctance to see the laws fully and faithfully executed.”

It’s important to note that the vacancies at the top of these agencies have nothing to do with the sequester, which is forcing many federal departments to trim back their spending levels.

It’s not solely Senate Republicans who are to blame for the headless government. Obama has failed to put forward nominees for some posts, and Light says the president is “moving at a snail’s pace” to make other nominations.

Light says the administration also has “the longest questionnaire in the presidential history for vetting people who might become nominees. It’s brutal.” That serves to discourage some people from wanting to become nominees in the first place.